Poppet valves are employed in internal combustion engines to admit air or air and fuel mixtures into a cylinder during an intake stroke, to let exhaust gasses out of cylinders during an exhaust stroke and to close a cylinder during compression and power strokes of a piston. The standard internal combustion engine has an intake poppet valve and an exhaust poppet valve for each cylinder. Large internal combustion engines and some high performance engines have multiple intake and exhaust poppet valves for each cylinder.
During the compression and power strokes of an internal combustion engine, poppet valves must make sealing contact with a valve seat to seal the cylinders. Failure to seal a cylinder will result in loss of efficiency and power. A bad leak may prevent an internal combustion engine from running. During a major overhaul of an internal combustion engine, the valve faces of the poppet valves are ground and polished in a valve grinder and the valve seats, which the poppet valves contact to seal the cylinders, are refaced with precision high seed grinding stones.
Poppet valves operate in very hostile environments. They are subjected to high temperatures, high pressures and the products of combustion. Deposits of carbon and other materials build up on the surfaces of a valve head and on portions of the valve stems adjacent to the valve head that are exposed to products of combustion. Most of the deposits are on the exhaust valve. However, there are deposits on the intake valve too. These deposits must be removed before the valve faces can be ground and polished. Failure to remove the deposits prior to grinding the valve face will reduce the useful life of the grinding stone and may interfere with the valve face grinding process.
Deposits of carbon and other material are commonly removed from poppet valves by hand holding the valves against a rotating wire wheel. A slight slip when holding a valve against a rotating wire wheel can result in contact between the hand and the rotating wire wheel and a hand injury. Hand cleaning, in addition to being dangerous, is slow. It takes substantial time to manually manipulate a valve to bring all surfaces with deposits into contact with a rotating wire brush and to remove the surface deposits. Poppet valves are also cleaned in dunk tanks with small metal balls and chemical cleaners. The chemical cleaners are expensive and produce vapors. Direct contact with the chemicals and with the vapors can cause injuries to workers that are cleaning poppet valves. Disposal of the chemicals after they become too contaminated for further use is expensive and can be difficult. The valve stems can be damaged by the metal balls and the toxic chemicals. A damaged valve stem surface will damage engine valve guides and lead to oil consumption and engine failure.